The objectives of this project are to survey the range of mycoplasma viruses, to characterize the biology of these viruses, and to examine their possible role in human disease. The specific goals for this proposal are in four areas: 1. replication and genetics of Group 1 viruses, 2. composition and virus-cell interactions of Group 2 viruses, 3. nature of the mycoplasma virus-cell carrier state, and 4. possible role of viruses in determining mycoplasma pathogenicity. In the first area, Group 1 replication studies will examine the synthesis of virus specific proteins and structure of viral assembly intermediates and genetic studies will determine the number of Group 1 complementation groups and begin physical mapping. For the second area, Group 2 virus DNA and membrane compositions will be investigated and intracellular replication will be studied. The third area will concern the nature of the carrier state and its virus-cell interactions that may affect mycoplasma pathogenicity.